Variable direction of view endoscopes allow the user to change the endoscopic viewing direction without having to change the position of the endoscope itself. Variable direction of view endoscopes come in two general classes: rigid and flexible. Such endoscopes are useful when the user wants to see structures which are beside or behind the tip of the endoscope but can not easily move the endoscope shaft because of anatomical constraints or constraints imposed by other surgical instruments in the operative field.
Variable direction endoscopy is desirable because it affords surgeons greater flexibility in their procedural approach. Increased viewing mobility improves the quality of diagnoses, as in cystoscopy for example, where a typical diagnostic screening involves inspecting the interior surface of the bladder for lesions or tumors. The ability to look laterally and retrograde is important when doing this type of diagnosis because it makes it possible to visually cover the entire bladder surface, including the entrance region near the bladder neck. In ear-nose-throat and neurosurgical procedures, variable viewing is desired because the procedures are delicate, and the entrance ports are small. It is therefore not possible to manipulate the endoscope significantly without injuring the patient. The ability to look sideways and backwards is important however during and after tumor resection when it is necessary to keep track of tumor fragments, which if not caught can nucleate new tumors. Laparoscopy, another surgical discipline, imposes fewer maneuvering constraints but still benefits markedly from variable direction viewing because it allows surgeons to get better observation angles during a procedure and increases diagnostic capabilities. Also, because of the greater viewing versatility, variable direction of view endoscopes can minimize conflicts with other tools and can simplify surgical planning by their ability to achieve standard viewing angles from nonstandard positions, allowing the surgeon to keep the endoscope “off to the side” but still get the desired view.
A fundamental feature of variable direction endoscopy is that it generally makes it possible for surgeons to eliminate “blind movements.” A blind movement is the process of moving an instrument inside a patient without being able to see where the instrument is heading. This can occur when it is necessary to advance a fixed-angle side viewing endoscope in its length direction without being able to see what is ahead of the scope, or when a surgical tool has to be manipulated at the boundary of the endoscopic field of view.
Generally, rigid scopes are easier for surgeons to control than flexible scopes. This is because there is a rigid connection between the tip of the endoscope and the surgeon's hand. When the surgeon moves her hand, the movement of the proximal end of the scope translates directly to the distal end of the scope, and it is easy for the user to develop a mental picture of how the scope tip moves based on her hand movement. This is not true of flexible endoscopes where the dynamic relationship between the distal and proximal ends of the scope is not always obvious. For this reason, use of flexible endoscopes often requires substantial training, and therefore many surgeons prefer rigid scopes if the situation permits.
Rigid and flexible scopes are typically designed for different applications, and they are not interchangeable. While flexible scopes have been widely adopted in the medical marketplace, rigid variable direction of view scopes have yet to establish themselves. A number of rigid variable direction of view endoscopes have been presented over the years, all with the goal of providing the surgeon with improved viewing mobility over traditional fixed-angle endoscopes. They have achieved this goal, but unfortunately their drawbacks have outweighed their advantages. For a given diameter the image quality delivered by a rigid variable direction of view endoscope is generally not as good as that delivered by a fixed-angle endoscope because some of the optical channel must be sacrificed in favor of the actuation mechanism, which also limits the field of view. The actuation mechanism adds complexity and cost to the design, manufacturing and assembly processes. The added mechanical complexity in turn reduces robustness and makes sterilization more difficult. Further, making variable direction of view endoscopes ergonomic and user-friendly is challenging. In several surgical disciplines, especially laparoscopy, it is necessary for the surgeon to be able to hold the endoscope flat across the patient's body in order to access certain parts of the anatomy. This practice requires that the endoscope have a minimal handle which is generally symmetric about the main axis of the endoscope. Therefore, gun-grip type handles are not suitable for surgical applications.
Another significant problem with current variable direction of view endoscopes (flexible or rigid with flex tip) is disorientation. As the endoscopic line of sight is changed, the user faces two difficulties. The first is keeping track of where the endoscope is “looking.” With a rigid fixed-angle endoscope it is relatively easy for the user to extrapolate the endoscopic viewing direction from the position of the endoscope shaft. This is not the case when the viewing direction is regularly changed relative to the longitudinal axis of the endoscope; the user quickly loses track of spatial orientation within the anatomy being observed. The second difficulty is keeping track of what is “up” in the endoscopic image. Depending on the view-changing mechanism, the image will rotate relative to the surroundings, and the user frequently loses orientation. This disorientation is often not correctable, especially in variable direction of view scopes which have distal imagers and no facility for changing image orientation.
Given the difficulties of variable direction endoscopes, it is common for surgeons to utilize rigid endoscopes with fixed viewing angles. Surgeons rely heavily on knowing that a certain endoscope provides a 30 or 45 degree viewing angle. This preference for using multiple fixed angle endoscopes is due in part to the fact that a surgeon knows that for a particular endoscope they can dependably know what the anatomy should look like.
What is desired, therefore, is a variable direction of view endoscope with an actuation mechanism that reduces the complexity and cost of the device while also providing a device that is robust and provides for ease of sterilization. What is further desired is an actuation mechanism that minimizes the amount of optical channel that is sacrificed for the mechanism. What is also desired is a variable view endoscope that is ergonomic to improve the handling and ease of use of the device. What is still further desired is a variable view endoscope that assists the surgeon in maintaining spatial orientation when altering the viewing angle.